1. Field of the Invention
The present invention relates generally to the field of electrosurgery and, more particularly, to surgical devices and methods which employ high frequency voltage to cut and ablate tissue.
The field of electrosurgery includes a number of loosely related surgical techniques which have in common the application of electrical energy to modify the structure or integrity of patient tissue. Electrosurgical procedures usually operate through the application of very high frequency currents to cut or ablate tissue structures, where the operation can be monopolar or bipolar. Monopolar techniques rely on external grounding of the patient, where the surgical device defines only a single electrode pole. Bipolar devices comprise both electrodes for the application of current between their surfaces.
Electrosurgical procedures and techniques are particularly advantageous since they generally reduce patient bleeding and trauma associated with cutting operations. Current electrosurgical devices and procedures, however, suffer from a number of disadvantages. For example, monopolar devices generally direct electric current along a defined path from the exposed or active electrode through the patient""s body to the return electrode, which is externally attached to a suitable location on the patient. This creates the potential danger that the electric current will flow through undefined paths in the patient""s body, thereby increasing the risk of unwanted electrical stimulation to portions of the patient""s body. In addition, since the defined path through the patient""s body has a relatively high impedance (because of the large distance or resistivity of the patient""s body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying tissue along and surrounding this pathway.
Bipolar electrosurgical devices have an inherent advantage over monopolar devices because the return current path does not flow through the patient. In bipolar electrosurgical devices, both the active and return electrode are typically exposed so that they may both contact tissue, thereby providing a return current path from the active to the return electrode through the tissue. One drawback with this configuration, however, is that the return electrode may cause tissue desiccation or destruction at its contact point with the patient""s tissue. In addition, the active and return electrodes are typically positioned close together to ensure that the return current flows directly from the active to the return electrode. The close proximity of these electrodes generates the danger that the current will short across the electrodes, possibly impairing the electrical control system and/or damaging or destroying surrounding tissue.
The use of electrosurgical procedures (both monopolar and bipolar) in electrically conductive environments can be further problematic. For example, many arthroscopic procedures require flushing of the region to be treated with isotonic saline (also referred to as normal saline), both to maintain an isotonic environment and to keep the field of viewing clear. The presence of saline, which is a highly conductive electrolyte, can also cause shorting of the electrosurgical electrode in both monopolar and bipolar modes. Such shorting causes unnecessary heating in the treatment environment and can further cause non-specific tissue destruction.
Present electrosurgical techniques used for tissue ablation also suffer from an inability to control the depth of necrosis in the tissue being treated. Most electrosurgical devices rely on creation of an electric arc between the treating electrode and the tissue being cut or ablated to cause the desired localized heating. Such arcs, however, often create very high temperatures causing a depth of necrosis greater than 500 xcexcm, frequently greater than 800 xcexcm, and sometimes as great as 1700 xcexcm. The inability to control such depth of necrosis is a significant disadvantage in using electrosurgical techniques for tissue ablation, particularly in arthroscopic procedures for ablating and/or reshaping fibrocartilage, articular cartilage, meniscal tissue, and the like.
In an effort to overcome at least some of these limitations of electrosurgery, laser apparatus have been developed for use in arthroscopic and other procedures. Lasers do not suffer from electrical shorting in conductive environments, and certain types of lasers allow for very controlled cutting with limited depth of necrosis. Despite these advantages, laser devices suffer from their own set of deficiencies. In the first place, laser equipment can be very expensive because of the costs associated with the laser light sources. Moreover, those lasers which permit acceptable depths of necrosis (such as eximer lasers, erbium:YAG lasers, and the like) provide a very low volumetric ablation rate, which is a particular disadvantage in cutting and ablation of fibrocartilage, articular cartilage, and meniscal tissue. The holmium:YAG and Nd:YAG lasers provide much higher volumetric ablation rates, but are much less able to control depth of necrosis than are the slower laser devices. The CO2 lasers provide high rate of ablation and low depth of tissue necrosis, but cannot operate in a liquid-filled cavity.
For these and other reasons, improved systems and methods are desired for the electrosurgical ablation and cutting of tissue. These systems and methods should be capable of selectively cutting and ablating tissue, while limiting the depth of necrosis and limiting the damage to tissue adjacent to the treatment site.
2. Description of the Background Art
Devices incorporating radio frequency electrodes for use in electrosurgical and electrocautery techniques are described in Rand et al. (1985) J. Arthro. Surg. 1:242-246 and U.S. Pat. Nos. 5,281,216; 4,943,290; 4,936,301; 4,593,691; 4,228,800; and 4,202,337. U.S. Pat. Nos. 4,943,290 and 4,936,301 describe methods for injecting non-conducting liquid over the tip of a monopolar electrosurgical electrode to electrically isolate the electrode, while energized, from a surrounding electrically conducting irrigant. U.S. Pat. Nos. 5,195,959 and 4,674,499 describe monopolar and bipolar electrosurgical devices, respectively, that include a conduit for irrigating the surgical site.
U.S. Pat. No. 5,290,286 describes bipolar electrosurgical instruments including a pair of closely spaced conductive electrodes with distal curves to provide scoop-like excision in tissue. U.S. Pat. No. 5,035,696 describes a bipolar electrosurgical cutting wire for a retrograde sphincterotomy. The bipolar cutting wire may be powered using an electrosurgical generator designed to deliver high levels of output power into bipolar devices operating at low impedances. U.S. Pat. No. 4,034,762 describes a bipolar electrosurgical apparatus that utilizes square waves at output voltage levels of 200 to 400 volts with spikes in the waveform with peak voltage values of about 420 volts. U.S. Pat. Nos. 4,969,885 and 4,092,986 teach the advantages of using substantially constant voltage output electrosurgery generators.
The present invention provides a system and method for selectively applying electrical energy to structures within or on the surface of a patient""s body. The system and method allow the surgical team to perform electrosurgical interventions, such as ablation and cutting of body structures, while limiting the depth of necrosis and limiting damage to tissue adjacent the treatment site. The system and method of the present invention are particularly useful for surgical procedures within accessible sites of the body that are suitable for electrode loop resection, such as the resection of prostate tissue and leiomyomas (fibroids) located within the uterus, and for procedures within confined (e.g., narrow) spaces within the patient""s body, such as the spaces around the articular cartilage between the femur and tibia and the spaces between adjacent vertebrae in the patient""s spine.
The system according to the present invention comprises an electrosurgical probe having a shaft with a proximal end, a distal end, and at least one active electrode at or near the distal end. A connector is provided at the proximal end of the shaft for electrically coupling the active electrode to a high frequency voltage source. The active electrode includes at least one active portion having a surface geometry configured to promote substantially high electric field intensities and associated current densities between the active portion and the target site when a high frequency voltage is applied to the electrodes. These high electric field intensities and current densities are sufficient to break down the tissue by processes including molecular dissociation or disintegration. The high frequency voltage imparts energy to the target site to ablate a thin layer of tissue without causing substantial tissue necrosis beyond the boundary of the thin layer of tissue ablated. This ablative process can be precisely controlled to effect the volumetric removal of tissue as thin as a few layers of cells with minimal heating of or damage to surrounding or underlying tissue structures.
In an exemplary embodiment, the high electric field intensities at the active portion of the active electrode may be generated by positioning the active electrode and target site within an electrically conducting liquid, such as isotonic saline, and applying a high frequency voltage that is sufficient to vaporize the electrically conducting liquid over at least a portion of the active electrode in the region between the active portion of the active electrode and the target tissue. Since the vapor layer or vaporized region has a relatively high electrical impedance, it increases the voltage differential between the active electrode tip and the tissue and causes ionization within the vapor layer due to the presence of an ionizable species (e.g., sodium when isotonic saline is the electrically conducting fluid). This ionization, under optimal conditions, induces the discharge of energetic electrons and photons from the vapor layer and to the surface of the target tissue. A more detailed description of this phenomena can be found in application Ser. No. 08/561,958, filed on Nov. 22, 1996, the complete disclosure of which has already been incorporated herein by reference.
Suitable electrode surface geometries for producing sufficiently high electric field intensities to reach the threshold conditions for vapor layer formation may be obtained by producing sharp edges and/or corners at the active portion of the active electrode(s). Alternatively, the electrode(s) may be specifically designed to increase the edge/surface area ratio of the active portion. Electrode shapes according to the present invention can include the use of formed wire (e.g., by drawing round wire through a shaping die) to form electrodes with a variety of cross-sectional shapes, such as square, rectangular, L or V shaped, or the like. Electrode edges may also be created by removing a portion of the elongate metal electrode to reshape the cross-section. For example, material can be removed along the length of a solid or hollow wire electrode to form D or C shaped wires, respectively, with edges facing in the cutting direction. Alternatively, material can be removed at closely spaced intervals along the electrode length to form transverse grooves, slots, threads or the like along the electrodes.
Additionally or alternatively, the active electrode surface(s) may be modified through chemical, electrochemical or abrasive methods to create a multiplicity of surface asperities on the electrode surface. The asperities on the surface of the active electrode(s) promote localized high current densities which, in turn, promote bubble nucleation at the site of the asperities whose enclosed density (i.e., vapor density) is below the critical density to initiate ionization breakdown within the bubble. For example, surface asperities may be created by etching the active electrodes with etchants having a PH less than 7.0 or by using a high velocity stream of abrasive particles (e.g., grit blasting) to create asperities on the surface of an elongated electrode.
In a preferred embodiment, the system includes a return electrode spaced proximally from the active electrode. The return electrode may be integral with the shaft of the probe, or it may be separate from the shaft (e.g., on a liquid supply instrument). In an exemplary embodiment, the return electrode defines a liquid pathway for flow of electrically conducting liquid therethrough. The liquid is directed past the surface of the return electrode and over the active electrode to thereby provide a return current flow path between the target tissue site and the return electrode. A more complete description of methods and apparatus for generating a liquid current flow path between the active and returns electrodes can be found in application Ser. No. 08/485,219, filed on Jun. 7, 1995, the complete disclosure of which has previously been incorporated herein by reference.
In another aspect of the invention, the active electrode will also have a xe2x80x9cnon-activexe2x80x9d portion or surface to selectively reduce undesirable current flow from the non-active portion or surface into tissue or surrounding electrically conducting liquids (e.g., isotonic saline, blood or blood/non-conducting irrigant mixtures). Preferably, the xe2x80x9cnon-activexe2x80x9d electrode portion will be coated with an electrically insulating material. This can be accomplished, for example, with plasma deposited coatings of an insulating material, thin-film deposition of an insulating material using evaporative or sputtering techniques (e.g., SiO2 or Si3N4), dip coating, or by providing an electrically insulating support member to electrically insulate a portion of the external surface of the electrode. The electrically insulated non-active portion of the active electrode(s) allows the surgeon to selectively ablate tissue, while minimizing necrosis or ablation of surrounding non-target tissue or other body structures.
In one representative embodiment, an electrosurgical resecting instrument is provided having a resecting electrode on the distal end of a shaft and coupled to a high frequency voltage source. The resecting electrode is configured to fit within a working end of a resectoscope (discussed below) and to remove small portions of tissue (e.g., chips of tissue). Preferably, the loop electrode has an elongate body with first and second ends disposed near the distal end of the shaft to form a loop electrode for removing tissue portions and for providing visibility through the loop (i.e., with an optical viewing scope positioned within the resectoscope). The loop electrode may have a variety of shapes, e.g., V-shaped, square or the like. Preferably, the loop electrode has a semi-circular-shape to facilitate rapid resection of tissue chips from the target site.
The elongate body of the loop electrode includes an active portion with a surface geometry configured to promote substantially high electric field intensities and associated current densities between the active portion and the target site when a high frequency voltage is applied to the electrode. Preferably, the electric field intensities generated around the active portion of the loop electrode are sufficient to reach the threshold conditions for vapor layer formation between the electrode and the tissue, as discussed above. To that end, the active portion of the loop electrode can be formed with edges, corners, surface asperities or a combination thereof, to maximize the electric field intensities around the active electrode.
In a preferred configuration, the loop electrode will have a semi-cylindrical cross-section formed by, for example, removing material from a round or hollow tube to form two or more edges on one side of the loop electrode. Preferably, the edges will be oriented substantially parallel to the shaft so that they will face the tissue as the shaft is moved axially in the cutting direction. This orientation facilitates formation of the vapor layer between the electrode edges and the tissue. The opposite or non-active side of the electrode may include an insulating layer to selectively reduce undesirable current flow from the non-active portion into tissue or surrounding electrically conducting liquids.
In an exemplary embodiment, the elongate body of the resecting loop electrode lies in a plane that defines an obtuse angle with the shaft. In this way, the resecting loop electrode defines an obtuse angle with the usual cutting direction as the surgeon moves the resecting instrument parallel to the target tissue. Usually, the resecting loop electrode will define an angle of about 110xc2x0 to 160xc2x0 with the shaft, and preferably about 120xc2x0 to 140. This orientation increases the portion of the resecting loop electrode that is in contact with the tissue rather than exposed to electrically conducting liquid. Consequently, it significantly improves the ease of initiating the requisite conditions for formation of the vapor layer to ablate and cut tissue. In addition, this resecting loop electrode orientation increases the duration of electrode contact with tissue, thereby improving hemostasis of the resected tissue.
The resecting loop instrument of the present invention will usually include a return electrode for completing the current path between the active electrode and the tissue site. The return electrode may be formed on the shaft of the resecting loop electrode, on the resectoscope, or in a separate instrument. In a preferred configuration, the return electrode is formed on a separate return electrode oversheath that includes an electrically conducting hollow tube sized to receive the resecting loop shaft so that the active loop electrode extends beyond the distal end of the hollow tube. The return electrode tube is insulated on its inner and outer surfaces except for an exposed portion that is spaced proximally from the active electrode to generate a current flow path therebetween. The return electrode oversheath may include a liquid path for allowing electrically conducting liquid to flow over the exposed portion to facilitate the formation of the current flow path.
In an alternative embodiment of the resecting loop instrument, the return electrode sheath is insulated on its inner and outer surfaces except for an exposed portion that extends beyond (i.e., overhangs) the distal end of the sheath. The exposed portion generates a current flow path between the resecting loop electrode and the return electrode. If the return electrode is used in conjunction with and positioned over an insulated resecting loop shaft, the return electrode oversheath will be insulated on its outer surface only.
In an exemplary embodiment, the return electrode oversheath includes a proximal hub for connecting the oversheath to a conventional or specialized resectoscope, such as those commercially available from Circon/ACMI of Stamford, Conn. (under the tradename of xe2x80x9cUSA Elite System Resectoscopexe2x80x9d) and Olympus Corporation of Lake Success, N.Y. (under the tradename of xe2x80x9cOES Resectoscopexe2x80x9d, Model No. A-2012). In this configuration, the return electrode tube is sized to receive the resectoscope shaft, which usually includes a viewing lumen to provide viewing of the surgical site. The proximal hub will also include a suitable electrical connector for electrically coupling the return electrode to an electrosurgical generator.
In another representative embodiment, an electrosurgical ablation probe is provided having a shaft with a proximal end portion and a tongue-shaped distal end portion sized to fit within confined (e.g., narrow) spaces within the patient""s body, such as the spaces around the articular cartilage between the femur and tibia and the spaces between adjacent vertebrae in the patient""s spine. The probe includes at least one active electrode integral with or coupled to the tongue-shaped distal end portion and a connector on the proximal end portion for coupling the active electrode to an electrosurgical generator. The tongue-shaped distal end portion is substantially planar, and it offers a low profile, to allow access to confined spaces without risking iatrogenic injury to surrounding tissue, such as articular cartilage. Usually, the distal end portion will have a combined height (i.e., including the active electrode(s)) of less than 2 mm and preferably less than 1 mm.
In a specific configuration, the distal end portion of the probe has an active side and a substantially planar non-active side opposite the active side. The active electrode(s) are disposed on the active side, and are insulated from the non-active side to reduce undesirable current flow into tissue and surrounding electrically conducting fluids. In an exemplary embodiment, the non-active side of tongue-shaped end portion includes a substantially planar support member underlying and insulated from the active electrode(s). The support member provides support for the cantilevered electrode(s), and it has a substantially smooth, atraumatic surface opposite the active electrode(s) to minimize damage to tissue.
The active electrode(s) will usually be formed with edges, corners, surface asperities or the like to maximize the electric field intensities around the electrode surfaces. In a preferred configuration, the probe includes a plurality of active electrodes extending axially from the distal end of the shaft and having a semi-cylindrical cross-section formed by, for example, removing material from a round or hollow tube. The electrodes are spaced from each other and supported by the underlying tongue-shaped support member. The edges formed by the semi-cylindrical cross-section will face away from the support member to form an active, high electric field intensity zone for ablation of tissue. In an exemplary embodiment, the electrodes are electrically isolated from each other and coupled to current-limiting elements or circuitry to limit current flow based on the impedance between the active electrode and the return or dispersive electrode.
Similar to previous embodiments, the planar ablation probe will usually include a return electrode to facilitate operation in the bipolar mode. However, the probe can be utilized in the monopolar mode with a separate, dispersive electrode pad attached to the patient""s skin, for example. In one configuration, the shaft of the probe comprises an electrically conducting material with an insulating layer covering the conducting material to protect surrounding tissue from electric current. The shaft includes an exposed portion spaced proximally from the active electrode(s) to generate a current return path therebetween.